This is an old post, preserved for reference.
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Time for a new phone. Apple or Android? Neither. One with a dial and a curly cord please. Back in 1979, we moved into a new house and it came with a brand new BT 746 phone. It's simple technology and still works well, and I've used it on and off for the last 35 years.
700 series phones. I made up a new line cord out of an old modem lead, but the rest was just screw terminal work.
As with any of these posts, use your common sense, do not attempt things like this if you are not confident you know what you are doing. Although mains voltages are not present there are still over 30V and should be treated with care.